diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bfe7a0e2..bde43788 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -23,6 +23,7 @@ jobs:
         - '3.2'
         - '3.3'
         - '3.4'
+        - '4.0'
         - ruby-head
         - truffleruby-head
         gemfile: